The object of this invention is to improve the U.S. patent application of Ser. No. 07/395,513 of the same title filed by this applicant. The No. 07/ 395,513 application comprises a turning bar 1 which is magnetized to keep steel balls 22 in the sidewise holes 23. Turning bar 1 forces said balls to move outward to push against the inner surface of a pipe, to form a circumferential projection as a pipe supporter is turned around. But the contacting dimension of the bar 1 with the balls 22 is quite small, and if the magnetism is not enough, the balls 22 can easily fall out. To improve this defect, this invention has been devised.